Klystrons are microwave amplifiers, invented at Stanford University before World War II, and since used extensively in power sources for electron accelerators used in Medicine and High Energy Physics; and in transmitters for radar, UHF television, and satellite communications. In a conventional Klystron, a cylindrical electron beam, confined by an electromagnet, traverses and interacts with a number of resonant cavities, amplifying an input signal by 30-60 dB. The cavities are electrically isolated from each other by the cylindrical beam drift tube, which is too small to propagate the operating frequency. The size of the drift tube and the optics of the electron “gun”, where the beam is generated, place an upper limit on the current, and hence the power, of the device.
The Sheet Beam Klystron (“SBK”) is a microwave power amplifier that was developed at the Stanford Linear Accelerator Center (“SLAC”) in the early 1990s as a lower cost alternative to conventional klystrons for a future collider requiring thousands of powerful microwave sources. Since then, a variety of scientific, commercial, and military applications, requiring very high average (or peak) power together with light weight, resulted in several funded efforts to build SBKs, all of which failed. A recent study at SLAC revealed an inherent instability in the SBK. Based on this study, a need exists for a modification in the SBK configuration, to make it a viable high-power microwave source.
In an SBK, the electron beam is flat and can be extended laterally; the beam can therefore carry a higher current with lower current density. In the original SLAC work beam confinement was accomplished with “periodic permanent magnet” focusing (“PPM”), which was facilitated because of the lower current density of SBKs. For reasons peculiar to periodic focusing in combination with a sheet beam, the PPM focused SBKs developed to date employed beams confined with a Brillouin, rather than a stronger field, which is the practice for PPM-focused travelling wave tubes. Brillouin is the lowest axial magnetic field force necessary to confine a cylindrical or sheet beam, by neutralizing the outward force produced by the space charge in the beam. A problem with existing SBKs, however, is that the wide drift tube supports propagating modes, which can be “trapped”, i.e. form standing waves with strong transverse electric fields that can drive the electron beam into the drift tube walls.
Today, deep seated shale deposits across the country are being exploited with hydrofracture or “fracking”, a controversial but effective process involving large quantities of water mixed with sand and proprietary chemicals. Fracking is under attack as a serious menace to the environment, but it is viewed as a potential answer to the dependence on imported oil.
A potential alternative to fracking is described in U.S. Pat. No. 7,828,057 and U.S. Patent Application Publication No. US2013/0213637, both of which are incorporated by reference herein in their entirety. The Patent discloses a process where hydrocarbons are extracted from a target formation, such as oil shale, oil (tar) sands, heavy oil and petroleum reservoirs, methods which cause fracturing of the containment hydrocarbon rock and liquefaction or vaporization of the by microwave energy directed by a radiating antenna in the target formation. The microwave power vaporizes the water within the shale layer, and if kerogen is present, it is heated for liquefaction or vaporization. The resulting steam breaks up the rock, releasing gas and oil. In the process, the shale matrix becomes more transparent to microwaves (its loss tangent is reduced) allowing microwave power to penetrate deeper into the shale, thus expanding the volume of exploited shale around the borehole. The antenna in the target area is connected via a transmission line to a high power klystron located on the surface and producing one-half megawatt or greater microwave energy at 2 Gigahertz or higher frequency. The published patent application (Pub. No. 2013/0213637) discloses the location of the klystron in the target area near the antenna.